Ink jet printers are known as a type of non-impact printer which has no physical contact with the surface on which it is printing. As the name "ink jet" suggests, an ink jet printer projects a jet of ink out of the print head through free air onto a surface to be printed. Due to its ability to print on various shaped and textured surfaces without contact, the ink jet technology finds new applications daily, especially in all types of industries which rely upon product marking, coding, dating or identification. Ink jet printing (text and graphic) has also developed considerably.
Ink jet technology falls into two main categories. One is continuous ink jet technology, according to which a stream of ink is continuously circulating from the body of the printer through the print head and back to the body of the printer. The ink is broken into drops at the nozzle and then deflected by electric charge to either reach the target or end up in a return block. The other technology is drop-on-demand, according to which droplets of ink are forced out of the nozzle only when needed, at an appropriate time. In some cases, the ink is ejected by heating a resistor which causes an air bubble to expand. When the bubble collapses, the droplet breaks off and the system returns to its original state. In other cases, the ink is ejected under pressure pulses caused by mechanically induced volumetric changes in the ink.
A typical drop-on-demand type ink jet printing system of the latter case is disclosed in U.S. Pat. No. 4,459,601 to Howkins. In Howkins, the volume of an ejection chamber is varied by a piezoelectric transducer that communicates with a moveable wall of the ejection chamber. The transducer expands and contracts to drive ink out through an orifice. A printing control voltage is applied to electrodes placed across the piezoelectric transducer to induce the expanding or contracting movements of the transducer.
Generally, in the above Hawkins structure, the transducers are placed in predetermined positions through an adhesive agent or the like to attach to the ejection chambers. Particularly in high quality printers, it is desirable to design an increased number of the nozzles for ejecting ink drops in an ink jet printer head. Since the dimension of the ink jet printer head is limited, the transducers, arranged in a densely packaged array, must be as small as possible. Therefore, in the case of a high-density ink-jet recording apparatus having a large number of nozzles, there is a limitation from the viewpoint of accuracy in aligning and bonding the transducers to their respective moveable walls. The adhesive layer interposed between the moveable wall and the piezoelectric transducer may lower the driving efficiency of the ink jet apparatus as well.
In addition, the conventional ink jet apparatus utilizes a separate transducer for each channel. A pair of electrical electrodes must also be formed individually in each transducer. Accordingly, to construct such a printer head, a large number of individual parts must be used, and a large number of steps are required to assemble the array. For these reasons, it has heretofore been impractical to manufacture a very high density ink jet printer head.